Aromatic aldehydes are useful in many applications since they have highly reactive aldehyde groups. Particularly, terephthalaldehyde having two aldehyde groups, see formula 1 below, is gaining focus as basic material of medicines, agrichemicals, pigments, liquid crystal polymers, conducting polymers, heat-resistant plastics, etc.

Terephthalaldehyde is a sublimable white solid having a molecular weight of 134.13 and a melting point of 114–116° C. It is known to be highly soluble in alcohols and be soluble in ether, alkali solutions and hot water.
Terephthalaldehyde, the material to be purified by the present invention, is prepared by known methods.
Hereunder is a brief description of the methods for preparing terephthalaldehyde.
Terephthalaldehyde can be prepared by dehydration of a chlorinated intermediate, hydrogenation of methyl terephthalate, oxidation of p-xylene in vapor phase, and so forth.
Terephthalaldehyde should be purified to high purity in order to be used in polymer synthesis or fine chemical process. For this purpose, such impurities as benzaldehyde, p-tolualdehyde and 4-hydroxybenzaldehyde should be removed.
Thus, the object of the present invention is to provide a method for purifying terephthalaldehyde obtained by conventional preparation methods to such a high purity as to be directly used in polymer synthesis or fine chemical process.
There are few reports of the purification methods of terephthalaldehyde for use in polymer synthesis or fine chemical process through effective removal of impurities.
U.S. Pat. No. 2,888,488 discloses a method for preparing terephthalaldehyde in which the product is purified by solvent extraction, drying and sublimation. However, this method entails a complicated process and uses chloroform, an environment-unfriendly compound, as solvent.
Japan Patent Laid-Open No. 2001-199910 discloses a method for recrystallizing aromatic aldehyde by cooling. But, this method is also limited in obtaining high-purity terephthalaldehyde.